MEDIUM NC#23 Stack
150. Evaluate Reverse Polish Notation
📖 Problem
Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, , and /. Each operand may be an integer or another expression. Note that division between two integers should truncate toward zero. It is guaranteed that the given RPN expression is always valid. That means the expression would always evaluate to a result, and there will not be any division by zero operation.
🧠 Visual Learning Aid
1 Model the input into the right structure
2 Choose the core technique and invariant
3 Execute step-by-step with a sample
4 Validate complexity and edge cases
JS/TS Refreshers
- •Array methods (`push`, `pop`, `shift`, `slice`)
- •Object/Map/Set usage patterns
- •Function parameter and return typing
Logical Thinking Concepts
- •Define invariants before coding
- •Check edge cases first (`[]`, single element, duplicates)
- •Estimate time/space before implementation
💡 Approach
- → Use stack to store operands
- → When encountering operator, pop two operands and apply operation
- → Push result back to stack
- → Final result is only element left in stack
- → Time: O(n), Space: O(n)
🧭 Prerequisites
🛠️ Hints & Pitfalls
Hints
- •Use stack to store operands
- •When encountering operator, pop two operands and apply operation
- •Push result back to stack
Common Pitfalls
- •Final result is only element left in stack
- •Time: O(n), Space: O(n)
🧪 Test Cases
Hidden tests on submit: 1
Test Case 1
Not run Input:
evalRPN(["2","1","+","3","*"]); Expected:
9 Test Case 2
Not run Input:
evalRPN(["4","13","5","/","+"]); Expected:
6 Test Case 3
Not run Input:
evalRPN(["10","6","9","3","+","-11","*","/","*","17","+","5","+"]); Expected:
22 📝 Code Editor
📤 Output